Add PTRACE_GETSIGINFO and PTRACE_SETSIGINFO

These new ptrace commands allow a debugger to control signals more precisely;
for instance, store a signal and deliver it later, as if it had come from the
original outside process or in response to the same faulting memory access.

include/linux/ptrace.h

@@ -26,6 +26,8 @@
 /* 0x4200-0x4300 are reserved for architecture-independent additions.  */
 #define PTRACE_SETOPTIONS	0x4200
 #define PTRACE_GETEVENTMSG	0x4201
+#define PTRACE_GETSIGINFO	0x4202
+#define PTRACE_SETSIGINFO	0x4203
 
 /* options set using PTRACE_SETOPTIONS */
 #define PTRACE_O_TRACESYSGOOD	0x00000001

include/linux/sched.h

@@ -400,6 +400,7 @@ struct task_struct {
 	struct backing_dev_info *backing_dev_info;
 
 	unsigned long ptrace_message;
+	siginfo_t *last_siginfo; /* For ptrace use.  */
 };
 
 extern void __put_task_struct(struct task_struct *tsk);

kernel/ptrace.c

@@ -286,6 +286,23 @@ static int ptrace_setoptions(struct task_struct *child, long data)
 	return 0;
 }
 
+static int ptrace_getsiginfo(struct task_struct *child, long data)
+{
+	if (child->last_siginfo == NULL)
+		return -EINVAL;
+	return copy_siginfo_to_user ((siginfo_t *) data, child->last_siginfo);
+}
+
+static int ptrace_setsiginfo(struct task_struct *child, long data)
+{
+	if (child->last_siginfo == NULL)
+		return -EINVAL;
+	if (copy_from_user (child->last_siginfo, (siginfo_t *) data,
+			    sizeof (siginfo_t)) != 0)
+		return -EFAULT;
+	return 0;
+}
+
 int ptrace_request(struct task_struct *child, long request,
 		   long addr, long data)
 {
@@ -301,6 +318,12 @@ int ptrace_request(struct task_struct *child, long request,
 	case PTRACE_GETEVENTMSG:
 		ret = put_user(child->ptrace_message, (unsigned long *) data);
 		break;
+	case PTRACE_GETSIGINFO:
+		ret = ptrace_getsiginfo(child, data);
+		break;
+	case PTRACE_SETSIGINFO:
+		ret = ptrace_setsiginfo(child, data);
+		break;
 	default:
 		break;
 	}

kernel/signal.c

@@ -1244,10 +1244,13 @@ int get_signal_to_deliver(siginfo_t *info, struct pt_regs *regs)
 		if ((current->ptrace & PT_PTRACED) && signr != SIGKILL) {
 			/* Let the debugger run.  */
 			current->exit_code = signr;
+			current->last_siginfo = info;
 			set_current_state(TASK_STOPPED);
 			notify_parent(current, SIGCHLD);
 			schedule();
 
+			current->last_siginfo = NULL;
+
 			/* We're back.  Did the debugger cancel the sig?  */
 			signr = current->exit_code;
 			if (signr == 0)
@@ -1258,7 +1261,10 @@ int get_signal_to_deliver(siginfo_t *info, struct pt_regs *regs)
 			if (signr == SIGSTOP)
 				continue;
 
-			/* Update the siginfo structure.  Is this good?  */
+			/* Update the siginfo structure if the signal has
+			   changed.  If the debugger wanted something
+			   specific in the siginfo structure then it should
+			   have updated *info via PTRACE_SETSIGINFO.  */
 			if (signr != info->si_signo) {
 				info->si_signo = signr;
 				info->si_errno = 0;